The present invention relates to an improvement in an electromagnetic pump of a type used for fuel supply in a vehicle.
Vehicles commonly turn over or fall sideways by collision or for other reasons due to the recent increase in traffic volume. In such a traffic accident, fuel often leaks from a fuel tank, causing fire and resulting in fatalities. For this reason, demand has arisen for minimizing risk of fuel leaks in an emergency and preventing vehicle fire. For this purpose, first type of conventional electromagnetic valves are proposed in Japanese Utility Model Publication Nos. 57-213 and 57-47438. In one conventional electromagnetic valve, a control valve body constituting a control valve is arranged to close an opening of a through hole serving as a flow path. The control valve body is arranged at the outlet port of a sleeve member for slidably supporting a plunger or at the end of the through hole of the plunger. In another conventional electromagnetic valve, a control valve body for closing an outlet opening of a sleeve member is formed integrally with a delivery valve disposed at an opening of a through hole of a plunger.
In order to improve pumping performance in conventional electromagnetic pumps of this type, pulsation caused by reciprocal movement of the plunger must be prevented. In a conventional electromagnetic pump having a cyindrical shape, suction and delivery pressure chambers are formed at the two ends of a cylindrical pump housing, and a damper chamber is formed by partitioning the inner space by a diaphragm or the like. The pulsation then is absorbed by the damper chamber.
In the first type conventional electromagnetic valves each with a control valve for fuel leakage prevention having the structure described above, the control valve is mounted at a position different from the mounting position of the delivery valve required therefor. The overall structure of the control valve is complicated, and the number of constituting members is increased. As a result, the electromagnetic valve and hence the pump as a whole have a large size.
In the second type conventional electromagnetic valve, the control valve is mounted integrally with the delivery valve. Although the number of constituting members can be decreased, the delivery valve receives a high resistance due to the fluid pressure and its own weight, so that opening/closing of the delivery valve is delayed and a suction pressure or delivery quantity is decreased, resulting in inconvenience. Furthermore, a biasing force of a return spring for reciprocating the plunger acts on the delivery valve, so that the fitting and seat surfaces of the valve are worn, thus presenting a valve function problem.
In the electromagnetic pumps described above, a pulsation absorption function for absorbing pulsation at the delivery side upon reciprocal movement of the plunger to take fuel in or to deliver it to the delivery side must be provided in addition to a fuel leakage prevention function in an emergency. However, conventional structures are complicated and result in large pumps of high cost. Not only operation of a carburetor float valve and various relief valves is interfered, but also noise tends to be produced. Optimal suction and delivery operations of the pump cannot therefore be expected. The adverse influence of pulsation typically occurs in a rectangular pump without a pulsation absorption chamber.
An electromagnetic pump of this type is recently mounted in a small car with a stroke volume of 1,000 cc or less. A compact, lightweight, low-cost pump is required which satisfies fuel leakage prevention and pulsation absorption needs as described above. However, no conventional electromagnetic valve can currently satisfy these requirements.